This invention relates generally to tuning mechanisms, and more particularly to detented type "memory" tuning systems for UHF television tuners.
Several techniques for providing detent type UHF television tuners are known. Several such systems are described in U.S. Pat Nos. 3,774,459 issued Nov. 27, 1973 to A. A. Valdettaro; 3,757,227 issued Sept. 4, 1973 to M. L. Weigel; 3,188,871 issued June 15, 1965 to R. E. Mentzer; 3,697,904 issued Oct. 10, 1972 to E. Mohri et al.; and 3,205,720 issued Sept. 14, 1965 to T. D. Smith. An example of a commercial memory type VHF tuner is the RCA KRK 72 RVS 8242 3. A memory type UHF tuner has also been built by German Phillips Ltd. The Phillips tuner is described in an article by J. Korn entitled "Neuartige Abstimmhilfen fur UHF" appearing in "FUNKSCHAU," Vol. 12, p. 326, 1962.
Whereas these systems provide detent type UHF tuners, the Valdettaro patent does not provide a memory type fine tuning system. A memory type fine tuning system is a system wherein each channel (or group of adjacent channels) has an independent fine tuning mechanism for providing independent fine tuning of each channel, the setting of which is maintained despite changes in channel selection. Other prior art systems provide memory type fine tuning, however, because the fine tuning mechanism is tunable over three channels and also serves as a channel selector, the resettability of each channel is marginal, and generally some degree of fine tuning adjustment is required after each channel change. Furthermore, the channel number displayed is not independent of the position of the fine tuning control, and a unique indication of the channel number is not provided.
Modern VHF tuners, such as the RCA unit referenced above, utilize a turret or a switch type tuner that has inherent detent positions. As a result, the problems encountered in converting the continuously variable motion of a UHF tuner to detented operation do not arise.
The Phillips UHF tuner is designed for the European UHF band and employs a separate fine tuning element for each UHF channel. Such a system is usable in Europe because the European UHF band contains only 40 channels. In the United States, where 70 UHF channels are provided, the use of a separate tuning element for each channel would result in a structure so large and complex as to be impractical.
Accordingly, it is an object of the present invention to provide a UHF tuning system wherein each detent position of the selector shaft corresponds to a different UHF channel, and wherein a memory type fine tuning mechanism is provided to allow independent fine tuning of groups of channels lying in adjacent detent tuning positions.
It is another object of the present invention to provide a detented UHF memory type tuning mechanism having a digital readout that uniquely displays the channel number corresponding to each channel independently of the setting of the fine tuning mechanism.
A further object of the present invention is to provide a detent type UHF tuning mechanism having a memory type fine tuning mechanism tunable over the frequency range of one television channel.
In accordance with a preferred embodiment of the invention, a UHF tuner having a continuously variable tuning shaft is coupled to a detented selector shaft by means of a reduction gear mechanism. The gear reduction ratio is chosen such that the selector shaft may be rotated several revolutions over the tuning range of the UHF tuner, and such that each detent position corresponds to one of the UHF channels in the tuning range. A rotatable turret having a plurality of cams mounted thereon is provided, and a fine tuning mechanism is provided for selectively engaging and rotating one of the cams. The particular one of the cams to be engaged is determined by the position of the rotatable turret. A cam follower is provided for coupling the cam that is positioned for engagement by the fine tuning mechanism to the UHF tuner to permit the UHF tuner to be tuned by each cam. The range over which the UHF tuner can be adjusted by any particular one of the cams is limited to less than the bandwidth of a television channel to prevent the tuner from being tuned to an adjacent channel by the fine tuning shaft. The memory function is provided by rotating the turret to bring a different cam into engagement with the cam follower for each UHF television station in the reception area and adjusting each cam to individually fine tune each UHF television station. The rotation of the turret is accomplished by means of a Geneva mechanism coupling the selector shaft and the turret. The Geneva mechanism serves to rotate the turret a predetermined increment to bring a different cam into engagement with the cam follower each time the selector shaft is advanced a predetermined number of detent positions. In order to prevent an unintentional readjustment of the cam during the rotation of the turret, a mechanism is provided to disengage the cam follower from the cam during rotation of the turret.